1. Field
Methods and apparatuses consistent with the exemplary embodiments relate to a three-dimensional (3D) image acquisition apparatus and a method of extracting depth information in the 3D image acquisition apparatus, and more particularly, to a depth information extracting method capable efficiently removing an error due to random noise, which may be generated from a light source, an optical modulator, and an image pickup device used in a 3D image acquisition apparatus.
2. Description of the Related Art
Recently, along with the development of 3D display devices capable of displaying images having a sense of depth and an increase of demands thereof, the importance of 3D content has become an object of great interest. Accordingly, a 3D image acquisition apparatus, such as a 3D camera, by which a general user can directly produce 3D content has been researched. Such a 3D camera should obtain depth information together with conventional two-dimensional (2D) color image information.
Depth information regarding distances between surfaces of objects and a 3D camera may be obtained by using a stereo vision method using two cameras or a triangulation method using structured light and a camera. However, in these methods, as a distance of an object is far, accuracy of the depth information significantly decreases, and these methods depend on a surface state of the object, and thus it is difficult to determine accurate depth information.
A time-of-flight (TOF) method is introduced to improve the above-described problem. TOF technology is a method of measuring a light flight time from when illumination light is irradiated onto an object to when light reflected from the object is received by a light receiver. According to TOF technology, a series of processing procedures for extracting depth information, such as projecting light of a specific wavelength (e.g., a near infrared ray of 850 nm) onto an object by using an illumination optical system including a Light Emitting Diode (LED) or a Laser Diode (LD), receiving light having the same wavelength as the specific wavelength, which is reflected from the object, by a light receiver, and modulating the received light by a modulator having an already known gain wavelength, are performed. According to such a series of processing procedures, variations of the TOF technology have been introduced.
In addition, in a light processing process for extracting depth information in the TOF technology, a method of performing pulse driving of a light source and an optical modulation device, a method using a specific waveform, such as a triangular wave (e.g., a ramp waveform), or a method using a sine wave is introduced. In addition, various methods of driving the light source and the optical modulation device are introduced according to used waveforms, and various algorithms for extracting depth information from the intensity of light are introduced.
In the TOF method described above, depth information is extracted by assuming an ideal environment without noise. However, random noise always exists in an actual light source, an actual optical modulator, and an actual image pickup device, such as a Charge Coupled Device (CCD), due to various causes, such as instability of a power source, heat, and an external electromagnetic wave. The random noise causes an error in the process of extracting depth information. To remove the random noise, it is required to acquire a plurality of images within a time period of a single frame and generate a single image by averaging the plurality of images. A least square fitting method using a pseudo-inverse matrix is, for example, generally used as an algorithm of averaging a plurality of images. However, since an image pickup device, such as a CCD, has many pixels, i.e., hundreds of thousands to tens of millions of pixels, a usage amount of a memory and a computation amount may increase exponentially to use the averaging method. Alternatively, a light source, an optical modulator, and an image pickup device in which random noise is extremely restrained may be used. However, in this case, a size and a manufacturing cost of a 3D image acquisition apparatus may be significantly increased.